WEDNESDAY, Nov. 5, 2008 (Health.com) — Postmenopausal women who have lost interest in sex may be able to bring their libidos back to life with a testosterone patch, according to new research published Wednesday in The New England Journal of Medicine.

However, the use of the male hormone to boost sex drive in women may not be risk-free. Four women in the study who were taking testosterone developed breast cancer, but none of the women on placebo did. It’s not clear whether this was a statistical blip or a warning sign that excess testosterone could cause or spur the growth of a malignancy. Some women also reported excess hair growth, although none stopped using the hormone for this reason.

Susan R. Davis, MD, PhD, of Monash University in Australia, and colleagues in the United States, Canada, and Sweden, evaluated two different doses of testosterone delivered by Procter & Gamble Pharmaceuticals’ Intrinsa patch. In 2004, a U.S. Food and Drug Administration (FDA) panel gave Intrinsa the thumbs down and called for larger, longer studies to ensure that the medication was safe, in addition to proving that it actually helped women’s sex lives.

As the new findings show, it did. Wearing the higher-dose testosterone patch boosted a woman’s “satisfying sexual experiences” by an average of 2.1 times every four weeks, compared to an increase of just 0.7 such experiences for women taking a placebo. Both testosterone doses used in the study seemed to increase desire and decrease distress.

“Although the change in activity is modest, that’s something that is appropriate and I think most women would be more than happy with it,” says study investigator Sheryl A. Kingsberg, PhD, chief of behavioral medicine at University Hospitals Case Medical Center in Cleveland. “They wanted to return to the level of desire they had in their premenopausal years, and that’s what they got.” Before starting treatment, the women in the study had been having satisfying sex about twice a month on average, Kingsberg points out; the higher-dose patch increased that to once a week.

“For most women and providers of health care for women, that modest benefit is clinically meaningful,” agrees North American Menopause Society president JoAnn V. Pinkerton, MD, a professor of obstetrics and gynecology at the University of Virginia, in Charlottesville, who did not participate in the study.